1. Field of the Invention
The present invention relates in general to ceramic bearings and more particularly to a ceramic bearing and metal shaft assembly for use in an atmosphere of a high temperature (about 200.degree. C. or more)
2. Description of the Prior Art
When a bearing made of metal is used in an atmosphere of a high temperature, it deteriorates in both the corrosion resistance and the strength and furthermore it cannot be lubricated by oil, grease, etc. For this reason, in case of use in such an atmosphere of a high temperature, a bearing made of ceramics is employed since it is superior in the corrosion and wear resistance. When the ceramic shaft is used, a shaft to be supported thereby needs to be formed from the same ceramics as the bearing or a material nearly equal in a coefficient of linear expansion to the ceramics.
A problem of the prior art bearing and shaft assembly is that there is a difficulty in forming the ceramic shaft into a complicated shape, and therefore when the ceramic shaft needs to have a complicated shape an expensive manufacturing cost inevitably results. If the shaft is formed from an ordinary metal as carbon steel, chromium-molybdenum steel, etc., a considerable thermal expansion differential is caused between the bearing and shaft when the assembly is used in an atomosphere of a high temperature. Such a thermal expansion differential will cause a considerable stress in the cerarmic bearing and in the worst case damage or breakage of same. Accordingly, the shaft made of an ordinary metal is undesirable for use together with the ceramic bearing in an atmosphere of a temperature equal to or higher than 200.degree. C.